The present invention is directed generally to novel systems and methods for performing sputter deposition, and to optical devices manufactured using such systems and methods.
Conventional pulsed target plasma sputtering systems generate their plasma via application of 10 to 500 kHz pulsed DC power to a sputter target. Most commonly, magnetic fields of several times 0.01 Telsa are disposed proximate to the target to intensify the plasma formed. During negative pulses, ions drawn from the plasma sputter the target, and material from the target is deposited on a substrate. It is believed that electrons from the plasma neutralize charge on the target during parts of the pulse cycle when the negative voltage is off. It is believed that in a conventional pulsed-target plasma sputtering apparatus, the target pulsing power supply must provide a high-voltage leading edge, for the purpose of ignition of the plasma, on every pulse. While it is believed that a system comprising the application of a-symmetric bi-polar DC pulse signals for such a purpose is known, such systems in the prior art require complicated circuitry and such systems fail to provide means for independently controlling the ion currents and the electron currents at the target. Moreover, since the plasma ignition is partly a stochastic event/process, there is a degree of process uncertainty and instability. It would be beneficial to provide a system that provides better control of the process without adding complex circuitry to the apparatus arrangement.
The present invention is directed to a system for performing sputter deposition on a substrate. Biasing circuitry biases the target with an a-symmetric bi-polar DC voltage pulse signal. The biasing circuitry is formed from a positive voltage source with respect to ground, a negative voltage source with respect to ground and a high frequency switch. At least one current sensor, coupled to the biasing circuitry, monitors a positive current and a negative current from the target during one or more cycles of the a-symmetric bi-polar DC voltage pulse signal. A control system, coupled to the at least one current sensor, varies the ion current independently from the electron current. The ion and electron sources create a continuous plasma that is proximate the target and the biasing circuitry causes the target to alternatively attract ions and electrons from the plasma. The ions attracted from the plasma sputter the target, and material from the target is deposited on the substrate. The electrons attracted from the plasma neutralize accumulated charge on the target. In one embodiment, the controller varies the a-symmetric bi-polar DC voltage pulse signal used to bias the target independently from the ion and electron currents. In this embodiment, target voltages and currents are tailored to optimize film deposition parameters.
The invention also includes an optical filter that is created by a disclosed method and process. The optical filter comprises a substrate, and material disposed on the substrate by the disclosed process and method.